The present disclosure is generally directed to methods and apparatus to treat an eye with a laser beam, including aligning a laser treatment with the eye. Although specific reference is made to centration of a surgical pattern on the apex of a curved patient interface, the methods and apparatus as described herein can be used in many applications in which a laser is used to treat material.
The eye is used for vision and has several tissues that allow a person to see. The cornea and lens of the eye form an image on the retina where the image is sensed. The refractive properties of the eye can be such that the image formed on the retina is less than ideal. For example, the eye may have less than ideal vision resulting from one or more refractive causes such as nearsightedness, far sightedness, and astigmatism.
Although many prior technologies have been proposed and used to correct vision of the eye, many of these prior technologies may provide less than ideal results in at least some instances. For example, with spectacles and contact lenses, a corrective lens is placed in front of the eye or on the cornea to improve the image formed on the retina. However, not all patients tolerate spectacles and contact lenses and these corrective lenses are only effective when worn by the patient. Also, spectacles and contact lenses may provide less than ideal correction of higher order aberrations of the eye such as spherical aberration and coma. Surgical treatments have been proposed and developed such as radial keratotomy (hereinafter “RK”), photorefractive keratectomy (hereinafter “PRK”) and laser assisted in situ keratomileusis (hereinafter “LASIK”). With RK, cuts may be made deep into the cornea, and although these cuts can provide an initial correction of vision, long term stability of RK treated eyes may be less than ideal in at least some instances. With PRK, healing of a layer of epithelium, which is removed for treatment, can take longer than would be ideal and may result in discomfort to the patient while the epithelium regenerates. Although LASIK can provide faster healing of the eye than PRK, in at least some instances cutting of the LASIK flap can be less than ideal, and applanation of the eye with a microkeratome may result in a temporary increase in intra-ocular pressure.
Laser surgery with ultra-short pulse lasers such as femtosecond lasers have been used to treat the eye. These pulsed lasers can make very accurate incisions of the eye and can be used in many ways to treat the eye. For example, short pulse lasers can be used to incise corneal tissue to make flaps with Femto-LASIK. Additional types of incisions that can be performed with the short pulse lasers include incisions for paracentesis, limbal relaxing incisions, and refractive incisions to shape the cornea, for example. The surgical incisions formed with ultra-short pulsed lasers can be quite accurate, and in at least some instances it can be helpful to hold the eye in position with a patient interface that couples the laser to the incised tissue of the eye such as the cornea. The patient interface can hold the eye in place so that an incision can be formed at the correct depth in the cornea. Prior patient interfaces have included a flat surface to contact the cornea. Although effective in facilitating cutting tissue at the intended depth, the flat patient interface may deflect the cornea more than would be ideal and provide less than ideal coupling to the cornea in at least some instances.
Although a patient interface with a curved surface to contact the cornea has been proposed, the prior methods and apparatus can provide less than ideal results in at least some instances. At least some of the prior treatments may result in an incision that is too deep, not deep enough, or both, in at least some instances. Curved patient interfaces can be difficult to align with the laser treatment and difficult to manufacture to within the tolerances of laser eye surgery. The alignment tolerances of the prior laser eye surgery systems may be less than ideally suited for use with a curved patient interface. In at least some instances, one or more components of the prior laser system can drift or move after alignment which can affect the accuracy of the placement of the cut profile, and the central treatment axis of the prior laser eye surgery systems may be difficult to define to within the tolerances appropriate for use with a curved patient interface.
In light of the above, it would be helpful to provide improved methods and apparatus to treat tissue. Ideally such methods and apparatus would overcome at least some of the above mentioned deficiencies of the prior methods and apparatus, for example by providing more accurate cutting of tissue without substantial deflection of corneal tissue and in a manner that can be used to treat many patients.